On 3/30/23 11:59 AM, Udipto Goswami wrote:
Hi Oliver,
On 3/17/23 5:26 PM, Udipto Goswami wrote:
Hi Greg, Oliver,
On 3/16/23 5:06 PM, Oliver Neukum wrote:
On 16.03.23 12:17, Greg Kroah-Hartman wrote:
On Thu, Mar 16, 2023 at 12:28:58PM +0530, Udipto Goswami wrote:
When the dwc3 device is runtime suspended, various required clocks
would
get disabled and it is not guaranteed that access to any registers
would
work. Depending on the SoC glue, a register read could be as benign as
returning 0 or be fatal enough to hang the system.
In order to prevent such scenarios of fatal errors, bail out of
debugfs
function is dwc3 is suspended.
Signed-off-by: Udipto Goswami <quic_ugoswami@xxxxxxxxxxx>
---
v3: Replace pr_err to dev_err.
drivers/usb/dwc3/debugfs.c | 60
++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
diff --git a/drivers/usb/dwc3/debugfs.c b/drivers/usb/dwc3/debugfs.c
index 850df0e6bcab..4a9d0994f3b4 100644
--- a/drivers/usb/dwc3/debugfs.c
+++ b/drivers/usb/dwc3/debugfs.c
@@ -544,6 +544,12 @@ static int dwc3_link_state_show(struct
seq_file *s, void *unused)
u32 reg;
u8 speed;
+ if (pm_runtime_suspended(dwc->dev)) {
+ dev_err(dwc->dev,
+ "Invalid operation, DWC3 suspended!");
+ return -EINVAL;
+ }
What prevents the device from being suspened right after you check
this?
I agree if the debugfs is access while suspend is in progress and lets
say the pm suspended status got reflected after the check. In this
case we will still run into the same fatal error scenario. But this
will be very tight race if in my understanding.
Our scenario was very simple, plug out the cable and try accessing the
debugfs. In this scenario at least the kernel should not crash.
Indeed. If you really need a semantics of not waking up the device if
somebody reads through debugfs, the attached patch should do the job.
But do you really need it?
Well, the intention was just to avoid the kernel crash. I believe in
any case the kernel should handle it gracefully and bail out. I
understand this patch won't help in the race condition which Greg
pointed out though.
Could you please suggest any other way which we can try out ?
Regards
Oliver
Apologies for the delay,
I checked with the patch you had attached,
drivers/usb/dwc3/debugfs.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/drivers/usb/dwc3/debugfs.c b/drivers/usb/dwc3/debugfs.c
index 850df0e6bcab..6922076572cd 100644
--- a/drivers/usb/dwc3/debugfs.c
+++ b/drivers/usb/dwc3/debugfs.c
@@ -543,13 +543,19 @@ static int dwc3_link_state_show(struct seq_file
*s, void *unused)
enum dwc3_link_state state;
u32 reg;
u8 speed;
+ int ret = 0;
+ if (!pm_runtime_get_if_in_use(dwc->dev)) {
Hi Oliver,
I think we need a little tweak here because as per this function's
description [1]:
int pm_runtime_get_if_in_use(struct device *dev);
- return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
runtime PM status is RPM_ACTIVE and the runtime PM usage counter is
nonzero, increment the counter and return 1; otherwise return 0 without
changing the counter
if it returns -EINVAL i think we still will go ahead and try accessing
the rest of the code.
How about something like this ?
- if (!pm_runtime_get_if_in_use(dwc->dev)) {
+ ret = pm_runtime_get_if_in_use(dwc->dev);
+ /* check if pm runtime get fails, bail out early */
+ if(ret < 0)
+ goto err_nolock;
+
+ if (!ret) {
ret = -EINVAL;
dev_err(dwc->dev,
"Invalid operation, DWC3 suspended!");
+ ret = -EINVAL;
+ dev_err(dwc->dev,
+ "Invalid operation, DWC3 suspended!");
+ goto err_nolock;
+ }
spin_lock_irqsave(&dwc->lock, flags);
reg = dwc3_readl(dwc->regs, DWC3_GSTS);
if (DWC3_GSTS_CURMOD(reg) != DWC3_GSTS_CURMOD_DEVICE) {
seq_puts(s, "Not available\n");
- spin_unlock_irqrestore(&dwc->lock, flags);
- return 0;
+ goto err;
}
reg = dwc3_readl(dwc->regs, DWC3_DSTS);
@@ -559,9 +565,11 @@ static int dwc3_link_state_show(struct seq_file *s,
void *unused)
seq_printf(s, "%s\n", (speed >= DWC3_DSTS_SUPERSPEED) ?
dwc3_gadget_link_string(state) :
dwc3_gadget_hs_link_string(state));
+err:
spin_unlock_irqrestore(&dwc->lock, flags);
-
- return 0;
+ pm_runtime_put(dwc->dev);
+err_nolock:
+ return ret;
}
This works for my usecase. Tested it and I don't see any fatal errors.
Can we consider mainlining it ? We will need to cover the other
functions as well in similar way. Can I proceed and make the change and
include your Suggested-by/Signed-off-by tag ?
Or do you want to push this on a separate one ?
Thanks,
-Udipto
[1]: https://www.kernel.org/doc/Documentation/power/runtime_pm.txt
Thanks,
-Udipto
